Laptops, CRT, certain LCD desktop monitors and smartphones are capable of high PPI. This page tests this by displaying images at a smaller than their native size. That means if you open this page on a high PPI device next to a normal 96 PPI one, there will be a difference of sharpness and detail. You can try it out on “normal” monitors by using the page zoom in your browser. Zoom in to 200% and you should clearly see the diffierence in the images. The logo of my site is also higher resolution than displayed.